This study deals with critical gaps in our understanding of the mucosal immune defenses of the female genital tract and the need to improve diagnosis, cure, and prevention of infection by Trichomonas vaginalis (TV), which is the most common nonviral sexually transmitted pathogen in the US and worldwide. The infection (trichomoniasis) affects 8-10 million Americans each year with serious medical, economic, and social consequences especially for women and children. The prevalence of TV is highest in women of reproductive age and in low-resource communities with an enormous racial disparity (1.5 to 10 times more prevalent in African-American women from urban communities). Among TV-attributable risks and pathologies disproportionately affecting minority populations are pre-term birth, low birth weight, cervical cancer, and higher risk of HIV. The estimated lifetime cost of treating trichomoniasis-attributable HIV infections is $167 million. Resistance to the current drug of choice, metronidazole, is rising to alarmingly high rates, and pregnant women treated with metronidazole are at even higher risk of pre-term birth. Almost half of TV-infected women are asymptomatic while the others develop a severe genital inflammation, which is an additional risk factor for HIV acquisition. The mechanisms of symptom disparity, lack of lasting immunity, high recurrence rate, and resistance to treatment are unknown. Several studies including ours have documented the presence of TV-specific dsRNA viruses (TVVs) in clinical isolates of the parasite, but little is known about their genetics, virulence, relevance to the inflammatory reaction, drug resistance, and medical complications of trichomoniasis. Our recently published data show the simultaneous presence of as many as 4 distinct species of TVVs in clinical TV isolates from women with vaginitis. Furthermore, we have demonstrated that in genital epithelial cells, TV strains harboring one or more TVVs induce a heightened, virus- dependent inflammatory response. We propose a novel hypothesis that implicates TVVs as modifiers of TV virulence and as factors underlying symptom disparity of TV infections and current therapy's side effects, thus emerging as key targets for prognostic/diagnostic biomarkers and new therapies. This hypothesis will be addressed by the following Specific Aims: (1) discover novel molecular determinants of TVV-TV-human interactions with impact on vaginal epithelial immune function (2) define genetic, biochemical, and biophysical characteristics of TVVs with impact on TV virulence and vaginal immune function that could be used for diagnostic or therapeutic approaches; (3) collect and examine clinically defined primary TV isolates to link distinct TVV genotypes and molecular characteristics to drug resistance and symptomatic trichomoniasis in a US population most vulnerable to TV-attributable disease. Our interdisciplinary approach includes a physiological in-vitro model system, novel molecular biology techniques and isogenic tools, as well as a survey of women seeking treatment for trichomoniasis. The proposed translational research will generate new basic knowledge of vaginal immunity and infection risk factors with high impact on women's and children's health.